The invention relates to a seal ring for sealing around a shaft and, more particularly, a combined static and dynamic seal ring.
Seal rings generally of the type to be described are disclosed in European patent application No. 12133. They are intended for sealing an air-liquid mixture and, particularly, for sealing an oil mist of the type frequently encountered in the crankcases of internal-combustion engines.
The principle of operation of seal rings of this type is based on a phase separation of the medium to be sealed in a compact which rotates with the shaft and is porous in the radial and axial directions. The medium to be sealed flows into the pore system of the compact and is rotationally accelerated radially. The forces which are exerted on the liquid constituents in this process are considerably greater than those which are exerted on the gaseous constituents because of the greater mass per unit volume of the liquids. As a result, the liquid constituents are immediately thrown radially and thus pumped back into the sealed space, while the gaseous constituents are able to flow nearly unhindered through the compact in the axial direction. Then they are likewise radially deflected and returned to the sealed space. The pressure level in the latter is stable under operating conditions. Liquid constituents are able to traverse the sealing ring only when the speed of rotation is reduced, and leakage is prevented in that case by a lip seal ring which then becomes effective.
A requirement for proper operation of the above seal is direct contact between the porous compact and an annular sealing surface which projects inwardly from an outer ring thereabout. Since the compact rotates under operating conditions, frictional forces of this contact must be overcome. This requires additional energy consumption and results in wear so that the seal ring described has only a limited service life.
U.S. Pat. No. 3,256,027 discloses a seal ring of the type in which a lip seal lifts off in operation. It is preceded, in the direction of the medium to be sealed, by a contact-free centrifugal seal. The later consists of an impeller which rotates with the shaft and an impingement surface which externally surrounds the impeller and extends parallel to the shaft axis. The impelled liquid striking the impingement surface is thus deflected, not only in the direction of the sealed space, but also in the other axial direction. This results in leakage. No mention is made of the sealing of a mixture of a liquid and a gas.